1. Field
The present disclosure relates generally to the manufacturing of composite objects and, in particular, to bladders used to form composite objects. Still more particularly, the present disclosure relates to a method and apparatus for reinforcing a bladder, which may be used for forming composite objects, with an insert.
2. Background
Stringers may be used to stiffen aircraft structures, such as, for example, without limitation, the fuselage of an aircraft. As used herein, a “stringer” may be a strip of material or structure to which a panel may be attached. In an aircraft, a stringer may be attached to a fuselage skin to transfer aerodynamic loads away from the fuselage skin. A stringer may also be referred to as a stiffener in some cases. A composite stringer is a stringer comprised of one or more composite materials.
Typically, a bladder may be used to form a composite stringer for an aircraft. The bladder used to form a composite stringer may be comprised of, for example, without limitation, rubber and/or other types of materials. In one illustrative example, one or more layers of composite material may be laid up over the bladder such that the layers of composite material conform to the outer shape of the bladder. This stackup of the layers of composite material may be referred to as a stringer layup. The stringer layup, supported by the bladder, may then be cured to form the composite stringer.
A hat stringer, also referred to as a hat stiffener, may have a cross-sectional shape that is similar to a hat. A hat stringer may have two webs, which are connected by a cap, that extend from a base. The base may be part of the hat stringer or may be the skin or panel to which the hat stringer may be attached.
The bladder that is used to form a hat stringer may have a cross-sectional shape that is a trapezoidal shape. In one example, a composite panel may be positioned at the base of the trapezoidal shape with the stringer layup positioned over the other three sides of the trapezoidal shape. The composite panel may extend substantially the entire length of the bladder. However, the composite panel may be longer than the stringer layup and may extend past at least one end of the stringer layup.
The stringer layup and the composite panel may be cured together with the bladder to both form the hat stringer and attach the hat stringer to the composite panel. The bladder may then be removed from the hat stringer-composite panel assembly. Because the composite panel is longer than the stringer layup, at least one end portion of the composite panel may not have any contact with the hat stringer. This end portion may be used to attach the composite panel to a different composite panel to form a splice joint.
Forming this splice joint may require that the end portion of the composite panel be substantially planar, or flat, within selected tolerances. However, in some cases, the end portion of the composite panel may be out-of tolerance. For example, without limitation, the bladder used to form the hat stringer may be a reusable bladder that has been used to form multiple hat stringers.
When the bladder is exposed to curing temperatures and/or pressures for an extended period of time, the bladder may change shape. For example, without limitation, the bladder may depress slightly. In other words, the bladder may begin to cave inwards. Once a bladder has depressed more than desired, an out-of-tolerance condition may be created after curing for the end portion of the composite panel where the splice joint is to be formed. Consequently, this end portion of the composite panel may need to be reworked in order to meet selected tolerances. This rework may be performed using a shim material, sanding, and/or some other type of component or operation to bring the composite panel within tolerances. This type of rework may be more time-consuming and labor-intensive than desired. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.